1. Field of the Invention
The present invention relates to a microlens transcription molding roller provided with a microlens molding surface on an outer circumference thereof, a manufacturing method and apparatus of the microlens transcription molding roller and a microlens optical sheet.
2. Description of Related Art
A microlens array has been used in a field of light-controlling by concentration, diffusion, reflection, diffraction and the like, e.g. in the field of liquid crystal display, light-coupling device and image input device.
The microlens array is a device provided with minute concave or convex sheet-arranged unit lenses having diameter of approximately 10-300 μm and depth of approximately 0.6-60 μm. The respective lenses are normally designed on a spherical surface or an aspheric surface in a manner axisymmetric with the center thereof.
In order to manufacture a transcription-molding roller of such a microlens array, a drilling method disclosed in Document 1 (JP-2002-144348A) has been conventionally known.
In the drilling method, a base is disposed in a manner three-dimensionally movable relative to a diamond tool rotated by a rotary drive. Initially, the base is moved toward the diamond tool to form one microlens molding cavity. Then, the base is moved away from the diamond tool in a constant direction to determine the next position of the tool. Subsequently, the base is moved toward the diamond tool to form the next microlens molding cavity. The above steps are repeated to provide a plurality of microlens molding cavities on the surface of the base.
Another known method is a roller-cutting processing method disclosed in Document 2 (“Ultra Precise Cutting of Die for Micro Lens Array using Diamond Cutting Tool (3)—Micro Patterning of High Accuracy Lens Array for Roll Die—” in Papers of Tutorial Lectures in 2007 Spring Semestrial Meeting of Japan Society for Precision Engineering: published in Mar. 1, 2007).
In the roller-cutting processing method, a roller is rotated around a roller shaft and an arc-tip diamond tool is moved toward and away from the roller at a high speed to sequentially form concave lens molding surfaces on the outer circumference of the roller. After the processing for one rotation of the roller is completed, the diamond tool is axially moved along the roller (normally by an interval for one lens) to be positioned, where the above operation is repeated to provide the lens molding surfaces on the outer circumference of the roller.
The drilling method disclosed in the Document 1 requires around one second for forming one lens molding surface. Accordingly, a great long time would be required for densely providing several tens-micron-size pattern on the entirety of a microlens pattern optical sheet.
On the other hand, in the roller-cutting processing method disclosed in the Document 2, the alignment accuracy of the lens pattern is influenced by a controlling process of the position for machining the lens pattern. In the method disclosed in the Document 2, the rotating position of the roller is recognized by an external position sensor and the diamond tool is advanced and retracted being triggered by a signal from the position sensor. Accordingly, the timing for advancing and retracting the diamond tool may vary in accordance with the sensitivity of the position sensor and transmission speed error of the trigger signal, which consequently results in deviation of processing position of the lens pattern.
Further, in the above method, after finishing the lens pattern processing for one rotation of the roller, the advancement and retraction of the diamond tool is stopped once, and, simultaneously, the diamond tool is moved axially along the roller by the length of one lens, where the lens-pattern machining for one rotation of the roller is conducted in response to the signal from the position sensor. Since the roller-cutting processing method requires repetition of the sequence of the operations, when the lens-patterning is conducted all over the roller, the processing is suspended while the lens-patterning is stopped and the diamond tool is moved, which results in deterioration of operation efficiency.